Control of CMP removal rate uniformity by selective heating of pad area

ABSTRACT

A CMP machine ( 100, 200, 300 ) and/or process that uses selective heating of the polishing pad/belt ( 120, 220, 320 ) to improve uniformity. A heating mechanism ( 110 ) is used to heat a selected area such as the perimeter ( 130, 230, 330 ) of the pad or belt ( 120, 220, 320 ). Heating the selected area improves the removal rate in that area. For example, heating along the perimeter of the pad ( 120, 220, 320 ) improves the removal rate at the perimeter of the semiconductor wafer ( 150 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The following co-pending application is related and hereby incorporated by reference: Serial No. Filing Date Inventor(s) TI-30582 Swanson

FIELD OF THE INVENTION

[0002] The invention is generally related to the field of semiconductor processing and more specifically to chemical-mechanical polishing semiconductor wafers.

BACKGROUND OF THE INVENTION

[0003] Chemical-mechanical polishing (CMP) for planarizing semiconductor wafers during fabrication is becoming more and more common. A CMP system generally consists of a polishing pad, wafer carrier, and slurry. As a wafer carrier positions a semiconductor wafer against the polishing pad, slurry is added between the polishing pad and the wafer. The wafer, the pad, or, more typically, both are moved to planarize the surface of the wafer. CMP employs both a mechanical removal of material (due to the physical abrasion of the polishing pad and slurry particles against the surface of the wafer) and a chemical removal (etch) of material (due to the chemical components of the slurry).

[0004] Three basic types of architecture are currently being manufactured. The first type is a rotary polisher. In a rotary polisher, the platen (and the polishing pad it holds) has a radius that is slightly larger than the diameter of the semiconductor wafer. Both the platen and the wafer are typically rotated. The second type of CMP machine is an orbital polisher. In an orbital polisher, the platen diameter is slightly larger than the wafer diameter. The wafer is rotated, but the pad is not. The wafer's center orbits around an axis of rotation offset slightly from the pad center. The third type of CMP machine is a linear belt polisher. In a linear belt polisher, a continuously fed belt is moved over the platen. The wafer is rotated during polishing.

[0005] The planarization uniformity on many polishing machines is difficult to control. This can be due to such process irregularities as pad conditioning, down force, and slurry delivery. Hence, achieving good planarization across a wafer is difficult. This is especially true for copper CMP, which is currently under development.

SUMMARY OF THE INVENTION

[0006] The invention is an improved CMP machine and/or process that uses selective heating of the polishing pad/belt to improve uniformity. A heating mechanism is used to create a temperature gradient across the polishing pad/belt by heating a selected area such as the perimeter of the pad or belt. Heating the selected area improves the removal rate in that area. For example, heating along the perimeter of the pad improves the removal rate at the perimeter of the semiconductor wafer.

[0007] An advantage of the invention is a CMP machine and/or process having improved planarization uniformity.

[0008] This and other advantages will be apparent to those of ordinary skill in the art having reference to the specification in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] In the drawings:

[0010] FIGS. 1A-1C are top views of a rotary polisher modified to include a heating mechanism according to the invention;

[0011] FIGS. 2A-2B are top views of an orbital polisher modified to include a heating mechanism according to the invention; and

[0012] FIGS. 3A-3B are top views of a belt polisher modified to include a heating mechanism according to the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0013] The invention will now be described in conjunction with three separate CMP machine architectures. It will be apparent to those of ordinary skill in the art that the invention may be applied to other machine architectures as well.

[0014] It is known that the copper removal rate during polish increases as the pad and slurry temperature rises. This is due to the fact that the chemical component of the CMP process is thermally activated. In the invention, the temperature of selective areas of the pad is adjusted to improve the uniformity across a wafer during CMP. For example, heat may be applied to selective areas the pad that correspond to areas of the wafer having a low removal rate.

[0015] In copper CMP removal rate is lower near the edges of a wafer (˜2-5 cm inset from the edge of the wafer by a few mm) than near the center of the wafer. In order to improve the removal rate uniformity across the wafer, the area of the polishing pad that polishes more of the edge of the wafer than the center is heated. The heat, in turn, increases the removal rate in that area making it more uniform across the wafer.

[0016] FIGS. 1A-C show a rotary polisher 100 modified to include a heating mechanism 110 for heating selective areas of the polishing pad 120. In a rotary polisher 100, the platen 140 had a radius that is slightly larger than the wafer 150 diameter. Platen 140 is used to hold pad 120. Wafer 150 is held against polishing pad 120 and rotated by a wafer carrier (not shown).

[0017] Heating mechanism 110 heats selective areas of the polishing pad 120 where an increased removal rate is desired. For example, in copper CMP the removal rate is lower near the edge of the wafer. Therefore, to improve this non-uniformity, the periphery 130 of the polishing pad 120 is heated since this area contacts the outer portions of the wafer 150.

[0018] Heating mechanism 110 may be located within platen 140 as shown in FIG. 1A. In this case, heating mechanism 110 could include an array of heaters 112. Alternative heating mechanisms will be apparent to those of ordinary skill in the art. For example, heating mechanism 110 may be located above pad 120, as shown in FIG. 1B. In this case, heating mechanism 110 may comprise radiant heaters 114 (e.g., lamps). Heating mechanism may alternatively comprise heated wires 116 embedded in selective areas of pad 120, as shown in FIG. 1C.

[0019] Heaters 112 are placed in areas of the platen where increased removal rate is desired. To improve copper CMP non-uniformity, heaters 112 are placed around the periphery of the platen to heat the overlying area 130 of the pad 120 that polishes the outer portions of the wafer 150. Of course, heaters may be placed throughout the platen for greater flexibility. Then, only those heaters below specific areas of the pad 120 could be used. Alternatively, heaters 114 may be placed above area 130 of pad 120 or wires 116 may be placed in area 130 of pad 120.

[0020] If desired, temperature monitoring may be used to actively control the temperature profile. For example, optical IR (infrared) radiometers 170 could be used to monitor the pad 120 surface temperature during CMP. The amount of heating could then be increased or decreased as desired to establish and maintain the proper temperature. Alternative means for temperature monitoring will be apparent to those of ordinary skill in the art.

[0021] In operation, slurry 160 is applied to the pad 120. Wafer 150 is pressed against pad 120 with the desired downforce and both the pad and wafer are rotated. Selected areas of the pad 120 are heated using heating mechanism 110 to improve the removal rate in those areas. For copper CMP, the periphery 130 of the pad 120 is heated. This results in a more uniform removal rate across the wafer 150. The temperature difference between the selected areas and the other areas of the pad may be on the order of 15° C. In the preferred embodiment, the selected areas are heated to a temperature of approximately 35-40° C. A maximum temperature is on the order of 70° C.

[0022] FIGS. 2A-B show an orbital polisher 200 modified to include a heating mechanism 110 for heating selective areas of the polishing pad 220. In an orbital polisher 200, the platen 240 had a diameter that is slightly larger than the wafer 150 diameter. Platen 240 is used to hold pad 220. Wafer 150 is held against polishing pad 220 and rotated by a wafer carrier (not shown).

[0023] As with the rotary polisher, heating mechanism 110 heats selective areas of the polishing pad 220 where an increased removal rate is desired. For example, in copper CMP the removal rate is lower near the edge of the wafer. Therefore, to improve this non-uniformity, the periphery 230 of the polishing pad 220 is heated since this area contacts the outer portions of the wafer 150.

[0024] Heating mechanism 110 may be located within platen 240 as shown in FIG. 2A. In this case, heating mechanism 110 could include an array of heaters 112, as discussed above. Alternative heating mechanisms will be apparent to those of ordinary skill in the art. For example, heating mechanism 110 may comprise heated wires 116 embedded in selective areas of pad 220, as shown in FIG. 2B. Radiant heating from above is difficult in this type of polisher because almost the entire pad 220 is covered by wafer 150 during polishing. The heat source would need to be placed above the wafer 150 in the wafer carrier.

[0025] If desired, temperature monitoring may be used to actively control the temperature profile. For example, thermocouples 280 located behind the wafer 150 or beneath the pad 220 may be used to provide feedback for effective process control. The amount of heating could then be increased or decreased as desired to establish and maintain the proper temperature. Alternative means for temperature monitoring will be apparent to those of ordinary skill in the art.

[0026] In operation, slurry 160 is applied to the pad 220 through holes in the pad 220. Wafer 150 is pressed against pad 220 with the desired downforce and both the pad 220 and wafer 150 are rotated. Selected areas of the pad 120 are heated using heating mechanism 110 to improve the removal rate in those areas. For copper CMP, the periphery 230 of the pad 220 is heated. The temperature difference between the selected areas and the other areas of the pad may be on the order of 15° C. In the preferred embodiment, the selected areas are heated to a temperature of approximately 35-40° C. A maximum temperature is on the order of 70° C. This results in a more uniform removal rate across the wafer 150.

[0027] A linear belt polisher 300 modified to include heating mechanism 110 is shown in FIGS. 3A-3B. Linear belt polisher 300 comprises a continuously fed belt 320. Wafer 150 is held against polishing belt/pad 320 and rotated by a wafer carrier (not shown).

[0028] Heating mechanism 110 heats selective areas of the polishing belt 320 where an increased removal rate is desired. For example, in copper CMP the removal rate is lower near the edge of the wafer 150. Therefore, to improve this non-uniformity, the outer portion 330 of the polishing belt 320 is heated since this area contacts the outer portions of the wafer 150.

[0029] Heating mechanism 110 may be located below the polishing belt 320, as shown in FIG. 3A or above, as shown in FIG. 3B. Heating mechanism 110 could include an array of radiant lamp heaters 114. Alternative heating mechanisms will be apparent to those of ordinary skill in the art. Heaters 114 are placed over or under the polishing belt 320 just prior to the belt 320 moving under wafer 150. To improve the removal rate at the outer regions of wafer 150, the heaters 114 are placed at the outer edges of polishing belt 320.

[0030] If desired, temperature monitoring may be used to actively control the temperature profile. For example, optical IR (infrared) radiometers could be used to monitor the pad 320 surface temperature during CMP. The amount of heating could then be increased or decreased as desired to establish and maintain the proper temperature. Alternative means for temperature monitoring will be apparent to those of ordinary skill in the art.

[0031] In operation, slurry 160 is applied to the pad 320. Wafer 150 is pressed against pad 320 with the desired downforce and both the pad and wafer are rotated. Selected areas of the pad 320 are heated using heating mechanism 110 to improve the removal rate in those areas. For copper CMP, the periphery 330 of the pad 320 is heated. The temperature difference between the selected areas and the other areas of the pad may be on the order of 15° C. In the preferred embodiment, the selected areas are heated to a temperature of approximately 35-40° C. A maximum temperature is on the order of 70° C. This results in a more uniform removal rate across the wafer 150.

[0032] While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims encompass any such modifications or embodiments. 

1. A method of fabricating an integrated circuit, comprising the steps of: placing a wafer against a moving polishing pad while adding a slurry and heating a selected portion of said polishing piece.
 2. The method of claim 1, wherein said polishing pad is a polishing belt.
 3. The method of claim 1, wherein said heating step is accomplished using a heating mechanism comprising a plurality of heat lamps to radiantly heat said polishing piece.
 4. The method of claim 1, wherein said polishing piece is a polishing pad and said heating is accomplished using heating wires placed within the polishing pad.
 5. The method of claim 1, wherein said selected portion comprises a peripheral area of said polishing piece.
 6. The method of claim 1, wherein said selected portion is heated to a temperature on the order of 35° C.
 7. The method of claim 1, wherein said heating step supplies a temperature gradient on the order of 15° C.
 8. A method of fabricating an integrated circuit, comprising the steps of: providing a partially fabricated wafer to a wafer carrier of a chemical-mechanical polish (CMP) machine; moving a polishing piece of said CMP machine; adding slurry to a surface of said polishing piece; placing said wafer against said surface while said polishing piece is moving; providing a temperature gradient across said surface of said polishing piece by heating a selected portion of said polishing piece using a heating mechanism.
 9. The method of claim 8, wherein said temperature gradient is about 15° C.
 10. The method of claim 8, wherein said heating mechanism comprises a plurality of heat lamps to radiantly heat said selected portion of said polishing piece.
 11. The method of claim 8, wherein said polishing piece is a polishing pad and said heating mechanism comprises heating wires placed within the polishing pad.
 12. The method of claim 8, wherein said selected portion comprises a peripheral area of said polishing piece.
 13. A chemical-mechanical polish (CMP) machine comprising: a platen; a polishing piece located over said platen; a wafer carrier for holding a wafer against said polishing pad; and a heating mechanism for establishing a temperature gradient across said polishing piece by heating a selected portion of said polishing piece.
 14. The CMP machine of claim 13, wherein said polishing pad comprises a polishing belt.
 15. The CMP machine of claim 13, wherein said heating mechanism comprises a plurality of heat lamps to radiantly heat said selected portion of said polishing piece. 